阅读说明：本技术 马达 (Motor with a stator having a stator core ) 是由 大西达也 岩野健彦 小川幸祐 瀬口敬史 于 2019-01-11 设计创作，主要内容包括：本发明的一个方式的马达具有：转子,其具有沿着在上下方向上延伸的中心轴线配置的轴,该转子能够绕中心轴线旋转；定子,其与转子在径向上隔着间隙而对置；以及壳体,其收纳转子和定子。壳体具有：筒状部,其沿中心轴线延伸；以及底部,其封闭筒状部的下侧的开口。在筒状部的内周面设置有嵌合部和锥形部,该嵌合部与定子嵌合,该锥形部位于比嵌合部靠下侧的位置并且直径随着朝向下侧而变小。在筒状部的外周面设置有轴向位置与锥形部重叠并沿周向延伸的凹部。(A motor according to one embodiment of the present invention includes: a rotor having a shaft disposed along a central axis extending in a vertical direction, the rotor being rotatable about the central axis; a stator facing the rotor with a gap in a radial direction; and a housing that houses the rotor and the stator. The housing has: a cylindrical portion extending along a central axis; and a bottom portion that closes the opening on the lower side of the cylindrical portion. A fitting portion to be fitted to the stator and a tapered portion having a diameter that decreases toward the lower side are provided on the inner peripheral surface of the cylindrical portion. A recess is provided on the outer peripheral surface of the cylindrical portion so as to overlap the tapered portion at an axial position and extend in the circumferential direction.)

1. A motor, comprising:

a rotor having a shaft disposed along a central axis extending in a vertical direction, the rotor being rotatable about the central axis;

a stator that is opposed to the rotor with a gap therebetween in a radial direction; and

a housing that houses the rotor and the stator,

the housing has:

a cylindrical portion extending along the central axis; and

a bottom portion that closes an opening on a lower side of the cylindrical portion,

a fitting portion to be fitted to the stator and a tapered portion having a diameter that decreases toward a lower side and located at a lower side than the fitting portion are provided on an inner peripheral surface of the cylindrical portion,

a recess extending in the circumferential direction is provided on the outer circumferential surface of the cylindrical portion, and the axial position of the recess overlaps with the tapered portion.

2. The motor of claim 1,

the thickness dimension of the cylindrical portion at the upper end of the recess is smaller than the thickness dimension of the cylindrical portion at the fitting portion.

3. The motor according to claim 1 or 2,

the bottom portion has a plurality of ribs extending radially inward from an inner peripheral surface of the cylindrical portion and arranged in a circumferential direction.

4. The motor of claim 3,

the upper end of the rib is located below the upper end of the recess.

5. The motor according to claim 3 or 4,

the rib has an inclined surface extending upward toward the radially outer side and continuing to the inner peripheral surface of the cylindrical portion.

6. The motor according to any one of claims 3 to 5,

a plurality of the ribs includes a 1 st rib and a 2 nd rib,

the 1 st rib extends in a radial direction with the same width,

the 2 nd rib has a base end portion located at a radially outer end portion and bulging in a circumferential direction,

a screw hole extending from a lower surface of the bottom is provided inside the base end portion.

7. The motor according to any one of claims 1 to 6,

the motor has a bearing that rotatably supports the shaft,

the bottom portion has a bearing holding portion that holds the bearing.

Technical Field

The present invention relates to a motor.

Background

Conventionally, a motor in which a stator and a housing are fixed by shrink fitting is known (for example, patent document 1).

Disclosure of Invention

Problems to be solved by the invention

The motor case is manufactured by, for example, die-casting a cylindrical shape and then cutting a portion requiring dimensional accuracy. In the case of manufacturing by die casting, the amount of metal material (e.g., aluminum alloy) used is directly related to the manufacturing cost.

In view of the above problems, an object of one embodiment of the present invention is to provide a motor having a housing in which the amount of material used is reduced, thereby reducing the manufacturing cost.

Means for solving the problems

A motor according to one embodiment of the present invention includes: a rotor having a shaft disposed along a central axis extending in a vertical direction, the rotor being rotatable about the central axis; a stator that is opposed to the rotor with a gap therebetween in a radial direction; and a housing that houses the rotor and the stator. The housing has: a cylindrical portion extending along the central axis; and a bottom portion that closes an opening on the lower side of the cylindrical portion. An inner peripheral surface of the cylindrical portion is provided with a fitting portion to be fitted to the stator, and a tapered portion which is located below the fitting portion and has a diameter that decreases downward. A recess extending in the circumferential direction is provided on the outer circumferential surface of the cylindrical portion, and the axial position of the recess overlaps with the tapered portion.

Effects of the invention

According to one embodiment of the present invention, there is provided a motor having a housing in which the manufacturing cost is suppressed by suppressing the amount of material used.

Drawings

FIG. 1 is a schematic cross-sectional view of a motor according to one embodiment.

FIG. 2 is a top view of one embodiment of a housing.

Fig. 3 is an external view of a housing according to an embodiment.

Detailed Description

Hereinafter, a motor according to an embodiment of the present invention will be described with reference to the drawings. In the drawings used in the following description, for the sake of easy understanding of the features, the features may be shown enlarged for convenience, and the dimensional ratios of the components are not necessarily the same as the actual ones.

In each figure, the Z-axis is shown as appropriate. The Z-axis direction in each drawing is a direction parallel to the axial direction of the central axis J shown in fig. 1. In the following description, the positive side (+ Z side, one side) in the Z-axis direction is referred to as "upper side", and the negative side (-Z side, the other side) in the Z-axis direction is referred to as "lower side". The upper and lower sides are directions for explanation only, and the actual positional relationship and directions are not limited. Unless otherwise specified, a direction parallel to the central axis J (Z-axis direction) is simply referred to as "axial direction" or "vertical direction", a radial direction about the central axis J is simply referred to as "radial direction", and a circumferential direction about the central axis J, that is, a direction around the central axis J is simply referred to as "circumferential direction". In the following description, the term "plan view" refers to a state viewed from the axial direction.

[ Motor ]

Fig. 1 is a schematic sectional view of a motor 1 of the present embodiment. The motor 1 includes a rotor 20, a stator 30, a housing 40, an upper bearing 6A, a lower bearing (bearing) 6B, and a bearing holder 10, wherein the rotor 20 has a shaft 21.

[ ROTOR ]

The rotor 20 is rotatable about the central axis J. The rotor 20 includes a shaft 21, a rotor core 24, and a rotor magnet 23.

The shaft 21 is disposed along a central axis J extending in the vertical direction (axial direction) with the central axis J as a center. The shaft 21 is supported by the upper bearing 6A and the lower bearing 6B so as to be rotatable about the center axis J.

The rotor core 24 is fixed to the shaft 21. The rotor core 24 circumferentially surrounds the shaft 21. The rotor magnet 23 is fixed to the rotor core 24. More specifically, the rotor magnet 23 is fixed to an outer surface of the rotor core 24 along the circumferential direction. The rotor core 24 and the rotor magnet 23 rotate together with the shaft 21.

[ STATOR ]

The stator 30 is opposed to the rotor 20 with a gap therebetween in the radial direction, and surrounds the rotor 20 on the radially outer side. The stator 30 includes a stator core 31, an insulator 32, and a coil 33.

The insulating member 32 is made of an insulating material. The insulator 32 covers at least a portion of the stator core 31. When the motor 1 is driven, the coil 33 excites the stator core 31. The coil 33 is formed by winding a coil wire (not shown). The coil wire is wound around the teeth of the stator core 31 via the insulator 32. The end of the coil wire is led out to the upper side.

The stator core 31 extends annularly around the center axis J. The outer peripheral surface of the stator core 31 is fixed to the inner peripheral surface 41a of the cylindrical portion 41 of the housing 40 by shrink fitting. That is, the stator 30 is fitted to the inner circumferential surface 41a of the housing 40.

[ Upper and lower side Bearings ]

The upper bearing 6A rotatably supports the upper end portion of the shaft 21. The upper bearing 6A is located on the upper side of the stator 30. The upper bearing 6A is supported by a bearing holder 10. The lower bearing 6B rotatably supports the lower end portion of the shaft 21. The lower bearing 6B is located on the lower side of the stator 30. The lower bearing 6B is supported by the housing 40.

In the present embodiment, the upper bearing 6A and the lower bearing 6B are ball bearings. However, the types of the upper bearing 6A and the lower bearing 6B are not particularly limited, and may be other types of bearings.

[ Bearings-holder ]

The bearing holder 10 is located on the upper side (+ Z side) of the stator 30. The bearing holder 10 supports the upper bearing 6A. The bearing holder 10 has a circular shape in plan view, for example, concentric with the central axis J. In fig. 1, the sectional shape of the bearing holder 10 is simplified.

The bearing holder 10 includes a circular plate 11 and an upper bearing holding portion 18 located at the center of the circular plate 11 in a plan view. The circular plate portion 11 is circular in plan view and extends in a plate shape along a plane perpendicular to the central axis J. The radially outer end of the disc portion 11 is fixed to the inner peripheral surface 41a of the housing 40. The upper bearing holding portion 18 holds the upper bearing 6A.

[ Shell ] for a refrigerator

The housing 40 houses the rotor 20 and the stator 30. The housing 40 has a cylindrical portion 41 and a bottom portion 45. The bottom portion 45 is located at one opening of the cylindrical portion 41.

The case 40 of the present embodiment is made of an aluminum alloy. The housing 40 may be made of other metal materials as long as it is made of metal materials that can be formed by die casting.

(cylindrical part)

The cylindrical portion 41 surrounds the stator 30 from the radially outer side. The cylindrical portion 41 is cylindrical and extends along the central axis J with the central axis J as the center. The cylindrical portion 41 has an inner circumferential surface 41a facing the inside in the radial direction and an outer circumferential surface 41b facing the outside in the radial direction.

The rotor 20 and the stator 30 are housed in the cylindrical portion 41. The inner peripheral surface 41A of the cylindrical portion 41 has a 1 st region 41A, a 2 nd region 41B, and a 3 rd region 41C. The 1 st region 41A, the 2 nd region 41B, and the 3 rd region 41C are arranged in this order from the upper side. The diameters of the 1 st region 41A, the 2 nd region 41B, and the 3 rd region 41C become smaller in this order. A 1 st stepped surface 41c facing upward is provided between the 1 st region 41A and the 2 nd region 41B. A 2 nd stepped surface 41d facing upward is provided between the 2 nd region 41B and the 3 rd region 41C.

The bearing holder 10 is fixed to the 1 st region 41A. In addition, a part of the lower end surface of the bearing holder 10 contacts the 1 st stepped surface 41c provided between the 1 st land 41A and the 2 nd land 41B. Thereby, the bearing holder 10 is positioned in the axial direction with respect to the housing 40.

A housing space a for housing a control unit (not shown) for controlling the rotation of the motor 1 is provided radially inside the 1 st region 41A and above the bearing holder 10. The control unit is connected to a coil wire extending from the stator 30 in the housing space a.

The 2 nd region 41B surrounds the stator 30 from the radially outer side. The 2 nd region 41B is provided with a fitting portion 44 to be fitted to the stator core 31. The cylindrical portion 41 holds the stator 30 in a fitting portion 44 provided on the inner circumferential surface 41 a. In addition, a part of the lower end surface of the stator core 31 contacts the 2 nd step surface 41d provided between the 2 nd region 41B and the 3 rd region 41C. Thereby, the stator 30 is positioned in the axial direction with respect to the housing 40.

The housing 40 is formed by die-casting a cylindrical shape, and then performing cutting such as drilling or turning on a portion requiring dimensional accuracy. The inner peripheral surface 41A is formed by first machining a region (1 st region 41A and 2 nd region 41B) above the 2 nd step surface 41d in a cutting step, and then further machining a region (1 st region 41A) above the 1 st step surface 41c in a cutting step. Therefore, the 3 rd region 41C is not machined. That is, the 3 rd region 41C is a region formed by die casting. Similarly, the outer peripheral surface 41b of the cylindrical portion 41 is not cut. That is, the outer peripheral surface 41b of the cylindrical portion 41 is a region formed by die casting.

Since the cylindrical portion 41 is formed by die casting, a tapered shape whose diameter becomes smaller as it approaches the bottom portion 45 is provided on the inner peripheral surface 41a of the cylindrical portion 41. Since the 1 st region 41A and the 2 nd region 42B of the inner peripheral surface 41A are cut, a tapered shape due to die-casting does not remain. However, since the 3 rd region 41C is not cut, a tapered shape due to die-casting remains. That is, the tapered portion 43 having a diameter that decreases downward is provided on the inner peripheral surface 41a of the cylindrical portion 41. The cylindrical portion 41 is a portion provided with the tapered portion 43, and the thickness dimension thereof increases toward the lower side. The tapered portion 43 is located in the entire 3 rd region 41C. The tapered portion 43 is located below the fitting portion 44.

A recess 41e extending in the circumferential direction is provided at a lower end portion of the outer peripheral surface 41b of the cylindrical portion 41. The recess 41e is open radially outward. The recess 41e extends in the circumferential direction. The axial position of the recess 41e overlaps with the tapered portion 43.

The cylindrical portion 41 is provided with a thin portion 42 whose thickness is reduced by providing a recess 41e on the outer circumferential surface 41 b. As described above, the tapered portion 43 is provided in the entire region of the 3 rd region 41C. On the other hand, the depth of the recess 41e is uniform in the axial direction. Therefore, the thickness dimension of the thin portion 42 increases toward the lower side. The thickness dimension of the thin portion 42 is smallest at the upper end of the thin portion 42. The thickness d2 of the cylindrical portion 41 at the upper end of the thin portion 42 is smaller than the thickness d1 of the cylindrical portion 41 at the portion where the fitting portion 44 is provided (d1 > d 2).

According to the present embodiment, the outer peripheral surface 41b of the cylindrical portion 41 is provided with a recessed portion 41e overlapping with the tapered portion 43. This can reduce the thickness of the tapered portion 43, and can suppress the amount of metal material used for the housing 40. In the production by die casting, since the amount of the metal material used directly relates to the production cost, the motor 1 can be provided at a low cost by suppressing the amount of the metal material used.

If a thick portion is provided in a part manufactured by die casting, pores are likely to be generated in the thick portion. When the air holes are generated in the interior of the member, the strength of the member is reduced. According to the present embodiment, the concave portion 41e is provided in a portion overlapping with the tapered portion 43. Therefore, the wall thickness can be prevented from becoming excessively large by the tapered portion 43, and the occurrence of pores inside can be prevented. This can sufficiently secure the strength of the case 40. Further, since the concave portion 41e is recessed radially inward, the housing can be gripped by clamping or the like in the manufacturing process of the motor.

According to the present embodiment, the cylindrical portion 41 is provided with the thin portion 42, and the thin portion 42 is located between the bottom portion 45 and the fitting portion 44 in the axial direction and extends in the circumferential direction. The thickness d2 of the cylindrical portion 41 at the upper end of the thin portion 42 (i.e., the upper end of the recess 41 e) is smaller than the thickness d1 of the cylindrical portion 41 at the fitting portion 44. Therefore, the thin portion 42 has lower rigidity than the fitting portion 44. As described above, the stator core 31 is fitted into the fitting portion 44 by the shrink fit. In the fitting portion 44, a radially outer stress is applied from the stator core 31 to the cylindrical portion 41. Therefore, the cylindrical portion 41 is slightly deformed in the direction in which the upper opening is opened. As will be described later, the bottom portion 45 holds the lower bearing 6B. If the deformation of the bottom portion 45 becomes large, the holding of the lower bearing 6B by the bottom portion 45 may become unstable.

According to the present embodiment, the thin portion 42 having low rigidity is provided between the bottom portion 45 and the fitting portion 44. Therefore, the thin portion 42 is preferentially deformed, and the deformation of the cylindrical portion 41 at the time of the shrink fit can be suppressed from being transmitted to the bottom portion 45. This reduces the amount of deformation of the bottom portion 45, and improves the stability of the holding of the bottom portion 45 to the lower bearing 6B.

(bottom)

Fig. 2 is a top view of the housing 40. The bottom portion 45 is disposed inside the cylindrical portion 41. The bottom portion 45 closes the opening on the lower side of the cylindrical portion 41. The bottom portion 45 has a bottom main body 46, a lower bearing holding portion (bearing holding portion) 48, a plurality of ribs 47a, 47b, and a plurality of protrusions 49a, 49 b.

As shown in fig. 1, the bottom main body 46 extends radially inward from the inner peripheral surface 41a of the cylindrical portion 41. The bottom body 46 extends along a plane perpendicular to the central axis J. The bottom main body 46 is located radially between the lower bearing holding portion 48 and the inner peripheral surface 41a of the cylindrical portion 41. The bottom body 46 has a generally circular shape in plan view.

A plurality of screw holes 45a, 45b are provided in a lower surface 46b of the bottom main body 46 (i.e., a lower surface of the bottom 45). The plurality of threaded holes 45a, 45b include a 1 st threaded hole 45a and a 2 nd threaded hole 45 b. The 1 st screw hole 45a is deeper than the 2 nd screw hole 45 b. Screws (not shown) for fixing the motor 1 to an external device (not shown) are inserted into the screw holes 45a and 45 b.

As shown in fig. 2, in the present embodiment, six 1 st screw holes 45a and two 2 nd screw holes 45b are provided in the housing 40. The 1 st and 2 nd screw holes 45a and 45b extend upward in the axial direction from the lower surface 46 b.

The six 1 st screw holes 45a are arranged on a pitch circle centered on the central axis J. Similarly, the two 2 nd screw holes 45b are arranged on a pitch circle centering on the central axis J. The pitch circle of the 1 st screw hole 45a is slightly larger than the pitch circle of the 2 nd screw hole 45 b. In the present embodiment, the 1 st screw holes 45a arranged in the circumferential direction are not uniformly spaced from each other. Similarly, the 2 nd screw holes 45b arranged in the circumferential direction are not uniformly spaced from each other.

As shown in fig. 1, the lower bearing holding portion 48 is located at the center of the bottom main body 46 in plan view. The lower bearing holding portion 48 holds the lower bearing 6B. The lower bearing holding portion 48 includes a cylindrical portion 48a extending in the axial direction about the central axis J, and a lower end projecting portion 48b extending radially inward from the lower end of the cylindrical portion 48 a. The lower bearing 6B is disposed radially inward of the cylindrical portion 48 a. The cylindrical portion 48a holds the outer ring of the lower bearing 6B from the circumferential outside. The lower end projection 48B contacts the lower end of the outer ring of the lower bearing 6B. The lower end projection 48B positions the lower bearing 6B in the axial direction. A hole 48c penetrating in the axial direction is provided at the center of the lower end protrusion 48b in a plan view. The shaft 21 is inserted through the hole 48 c.

The projections 49a, 49b are provided on the upper surface 46a of the bottom main body 46. The convex portions 49a, 49b protrude upward from the upper surface 46 a. The convex portions 49a, 49b protrude radially inward from the inner peripheral surface 41a of the cylindrical portion 41.

As shown in fig. 2, the projections 49a, 49b include the 1 st projection 49a and the 2 nd projection 49 b. The case 40 of the present embodiment is provided with one 1 st projection 49a and two 2 nd projections 49 b. The 1 st projection 49a has an axial dimension larger than that of the 2 nd projection 49 b. The 1 st projection 49a is provided with a tip portion of the 1 st screw hole 45a therein. Further, the 2 nd projection 49b is provided with a tip portion of the 2 nd screw hole 45b therein.

Ribs 47a, 47b are provided on the upper surface 46a of the base body 46. The ribs 47a, 47b protrude upward from the upper surface 46 a. The ribs 47a, 47b extend linearly in the radial direction. The ribs 47a, 47b connect the inner peripheral surface 41a of the cylindrical portion 41 and the outer peripheral surface of the cylindrical portion 48a of the lower bearing holding portion 48. The plurality of ribs 47a, 47b are arranged at equal intervals in the circumferential direction.

According to the present embodiment, the bottom portion 45 has the plurality of ribs 47a, 47b extending radially inward from the inner peripheral surface 41a of the cylindrical portion 41, and therefore the rigidity of the bottom portion 45 is improved. Therefore, even when the cylindrical portion 41 is deformed by the shrink fitting of the stator core 31, the deformation of the bottom portion 45 can be suppressed. This can improve the reliability of the holding of the lower bearing 6B by the lower bearing holding portion 48.

As shown in fig. 1, the upper ends of the ribs 47a and 47b are located below the upper end of the thin portion 42 of the cylindrical portion 41. As described above, the thin-walled portion 42 has the smallest wall thickness dimension at the upper end. By positioning the upper ends of the ribs 47a and 47b below the upper end of the thin portion 42, the ribs 47a and 47b do not increase the rigidity of the thinnest portion of the thin portion 42. Therefore, the upper end of the thin portion 42 is preferentially deformed, and the deformation of the cylindrical portion 41 due to the shrink fitting can be suppressed from being transmitted to the bottom portion 45.

As shown in fig. 1, the ribs 47a, 47b have inclined surfaces 47 d. The inclined surface 47d extends upward as it goes radially outward and is continuous with the inner peripheral surface 41a of the cylindrical portion 41. The ribs 47a, 47b have the inclined surfaces 47d, thereby improving the rigidity of the cylindrical portion 41. This can suppress vibration of the housing 40 caused by rotation of the rotor 20.

In the present embodiment, the inclined surface 47d is a curved surface that is curved with a predetermined radius of curvature. The inclined surface 47d may be a flat surface inclined at a constant inclination angle. However, by forming the inclined surface 47d as a curved surface smoothly connected to the inner peripheral surface 41a of the cylindrical portion 41, the rigidity of the cylindrical portion 41 can be more effectively improved.

As shown in fig. 2, the ribs 47a, 47b include the 1 st rib 47a and the 2 nd rib 47 b. The case 40 of the present embodiment is provided with two 1 st ribs 47a and four 2 nd ribs 47 b. The housing 40 of the present embodiment has an outer rib 50.

The 1 st rib 47a has a 1 st rib main body 47aa extending in the radial direction with the same width. The 1 st rib 47a extends in the radial direction with the same width. On the other hand, the 2 nd rib 47b has: a base end portion 47bb located at a radially outer end portion and bulging in the circumferential direction; and a 2 nd rib main body 47ba extending from the base end portion 47bb toward the radially inner side with the same width.

The tip portion of the 1 st screw hole 45a is provided inside the base end portion 47bb of the 2 nd rib 47 b. Two 1 st screw holes 45a are provided in a base end portion 47bb of one 2 nd rib 47b of the four 2 nd ribs 47 b.

Since the 2 nd rib 47b has the base end portion 47bb, the rigidity is high, and on the other hand, a metal material is often used. In contrast, since the 1 st rib 47a does not have the base end portion 47bb, the amount of the metal material used can be suppressed. According to the present embodiment, the 2 nd rib 47b having the base end portion 47bb and the 1 st rib 47a not having the base end portion 47bb are provided on the bottom portion 45. This can effectively increase the rigidity of the bottom portion 45 while suppressing the amount of metal material used as a whole.

As described above, the 1 st screw holes 45a are arranged at uneven intervals in the circumferential direction. Since the 1 st screw hole 45a is provided inside the 2 nd rib 47b, the ribs are arranged at uneven intervals in the circumferential direction, similarly to the 1 st screw hole 45 a. The 1 st rib 47a is disposed in a portion where a gap in the circumferential direction between the plurality of 2 nd ribs 47b arranged in the circumferential direction is large. This improves the rigidity of the bottom portion 45 and the cylindrical portion 41 in a balanced manner in the circumferential direction. Further, when the housing 40 is molded by die casting, the amount of the metal material filled in the circumferential direction can be made nearly uniform, and the dimensional accuracy of each portion can be improved.

While the embodiment and the modification of the present invention have been described above, the configurations and combinations thereof in the embodiment and the modification are examples, and addition, omission, replacement, and other modifications of the configurations can be made within the scope not departing from the gist of the present invention. The present invention is not limited to the embodiments.

The effects of the above embodiment can be obtained not only when the stator core 31 and the cylindrical portion 41 are fixed by shrink fitting but also when they are fixed by press fitting. That is, the stator core 31 may be fixed to the cylindrical portion 41 by press fitting.

Fig. 3 shows an external view of the housing of the present embodiment. As shown in fig. 3, the housing 40 has an outer rib 50. The outer rib 50 protrudes radially outward from the outer peripheral surface 41b of the cylindrical portion 41 and extends in the axial direction. The outer rib 50 is disposed in the center of the cylindrical portion 41. By providing the outer ribs 50, the rigidity of the cylindrical portion 41 can be improved. The outer rib 50 overlaps with the screw holes 45a, 45b in the circumferential direction. This can suppress stress applied to the housing 40 from the screw holes 45a and 45 b. The outer rib 50 is different in position from the recess 41e in the axial direction. The outer rib 50 is different in position from the recess 41e in the circumferential direction. The outer ribs 50 and the recesses 41e are alternately arranged in the circumferential direction. In fig. 3, there are two recesses 41e and two outer ribs 50, respectively. This can reduce the material of the case 40 while suppressing stress applied to the case 40 from the screw holes 45a and 45 b.

Description of the reference symbols

1: a motor; 6B: a lower bearing (bearing); 20: a rotor; 21: a shaft; 30: a stator; 40: a housing; 41: a cylindrical portion; 41 a: an inner peripheral surface; 41 b: an outer peripheral surface; 41 e: a recess; 43: a tapered portion; 44: a fitting portion; 45: a bottom; 45a, 45 b: a threaded hole; 47 a: the 1 st rib (rib); 47 b: the 2 nd rib (rib); 47 d: an inclined surface; 48: a lower bearing holding portion (bearing holding portion); 47 bb: a base end portion; d1, d 2: a thickness dimension; j: a central axis.